Implosion (mechanical process)

If the object was previously solid, then implosion usually requires it to take on a more dense form—in effect to be more concentrated, compressed, or converted into a denser material.

In an implosion-type nuclear weapon design, a sphere of plutonium, uranium, or other fissile material is imploded by a spherical arrangement of explosive charges.

This decreases the material's volume and thus increases its density by a factor of two to three, causing it to reach critical mass and create a nuclear explosion.

In the most common case, the innermost part of a large star (called the core) stops burning and without this source of heat, the forces holding electrons and protons apart are no longer strong enough to do so.

[2] The demolition of large buildings using precisely placed and timed explosions so that the structure collapses on itself is often erroneously described as implosion.